The present invention relates generally to packet switched digital telecommunication networks, and more particularly to such a network having improved systems for establishing connections for end-to-end communication between a host processor and remote transparent connection devices.
In 3270-type applications, polling takes place in which the Host computer or processor (Host) is coupled to a Host PAD (packet assembler/disassembler) that emulates the drops of various Control Units (CUs) and associated devices such as printers, displays or other terminal devices. As with most protocols, the polls are not transmitted through the network. Similarly, a Terminal PAD interacts with the CUs and their respective devices and conducts its polling with them locally.
In present-day 3270 applications, the process of setting up a connection to the Host calls for the terminal PAD to poll its CUs/devices and receive a special character or set of characters from the device to initiate the call. This requires that a user be present at the device to initiate the call. Even if the Terminal PAD has the address of the destination to which the call connection is to be made, it will not set up the call until the user's initiation.
In some applications employing the IBM 3270 system protocol, such as ATMs (automatic teller machines), there is no user per se--only an individual who enters a card to set up a connection with the Host. It would be desirable to set up the connection without requiring entry of a specific character by an operator. Also, when the terminal PAD polls the 3270 ATM, the ATM goes in service and recognizes the presence of a Host so that a card may then be inserted. If a call cannot be established to the Host, for whatever reason, the desired transaction cannot be completed by the customer. The user has no indication that the system is out of service, nor does the ATM recognize that a failure has occurred. It "sees" the poll and therefore assumes the Host is present and available. Here again, it would be desirable to have some technique to indicate that this is not the case.
It is therefore a principal object of the present invention to provide improvements in establishing end-to-end communication between a Host and devices employing 3270 protocol in an X.25 packet switched network.
It is another broad object of the present invention to provide apparatus and processes for establishing "transparent" connections as a preliminary to communication between devices at opposite ends of a packet switched network (PSN).